Two more rebreather patches

[Paul Sargent]

On Oct 27, 2014, at 06:10 PM, Rodrigo Severo <rodrigo at fabricadeideias.com> wrote:

> On Mon, Oct 27, 2014 at 1:43 PM, Paul Sargent <paul.lionseye at icloud.com> wrote:
> > Without knowing has much gas is in the loop (note: not counter lung size,
> > which is part of the maximum loop volume) you can't know how much diluent to
> > add to maintain it*.
> >
> > Example: 5l of gas in the loop. Decend from surface to 10m (2bar). I need to
> > double the mass of gas in the loop to maintain volume, hence I need to add
> > 5l (surface equivalent mass**).
 
[...snip...]

> I believe this kind of thing could be usefull for dive planning if we
> decide to took the complex approach. But I'm afraid it could get
> REALLY complex with not much added benefit.
 
I tend to agree. I was only really going down that road to show how complex it got.
> As I mentioned before, for SAC calculation after the dive, the
> simplier method I proposed seems to me easier and precise enough.
>
> And if you have your diluent and oxygen SAC salculated using the
> simplier methods I proposed, you could use these same figures for dive
> planning. In this cenario, gas consumption on dive plans should be
> calculated using the same simplier methods.
 
Certainly for the moment I'd keep it simple. Personally I'd favour no numbers, rather than wrong ones, so I'd forget about computing constant rate O2 usage. It's just not that useful IMHO. It's too far removed from the amount of O2 I use on a dive, and gas planning the CCR part of a dive really isn't that big a deal compared to OC.

For example: A one hour dive should be 20bar (60 litres) out of a standard 3 litre cylinder - just calculating 1 litre a minute. That's just way off. I always use about ~50 bar on a ~40 metre dive, so I tend to make sure I've got at least 100 bar when I jump in.

(or have a missed a different method of calculating things in the various mails?)

Paul
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